Field of the Invention
The present invention relates to a touch sensing system, and more particularly, to a touch sensing system for division-driving a touch screen using a plurality of touch sensing integrated circuits (ICs).
Discussion of the Related Art
User interface (UI) is configured so that users are able to communicate with various electronic devices and thus can easily and comfortably control the electronic devices as they desire. Examples of the user interface include a keypad, a keyboard, a mouse, an on-screen display (OSD), and a remote controller having an infrared communication function or a radio frequency (RF) communication function. User interface technology has continuously expanded to increase user's sensibility and handling convenience. The user interface has been recently developed to include touch UI, voice recognition UI, 3D UI, etc.
The touch UI has been indispensably adopted in portable information appliances. The touch UI is implemented through a method for forming a touch screen on the screen of a display device.
As shown in FIGS. 1 to 3, a mutual capacitive touch screen TSP includes Tx lines Tx1 to Tx4, Rx lines Rx1 to Rx8 perpendicular to the Tx lines Tx1 to Tx4, and touch sensors formed between the Tx lines Tx1 to Tx4 and the Rx lines Rx1 to Rx8. Each touch sensor includes a mutual capacitance Cm. A touch sensing circuit supplies a driving signal to the Tx lines Tx1 to Tx4 and receives a touch sensor signal synchronized with the driving signal through the Rx lines Rx1 to Rx8. The touch sensing circuit senses a change amount of charges of the touch sensor and analyzes the change amount of charges. Hence, the touch sensing circuit decides whether or not there is a touch input and finds out a position of the touch input when there is the touch input.
In the large-sized touch screen TSP, a large number of Tx lines are used. The large-sized touch screen TSP is connected to a plurality of touch sensing integrated circuits (ICs) IC#1 and IC#2 and may be dividedly driven. The touch sensing circuit is integrated into the touch sensing ICs IC#1 and IC#2. Receiving channels (hereinafter referred to as “Rx channels”) of the first touch sensing IC IC#1 are connected to the first to fourth Rx lines Rx1 to Rx4 formed on the left half of the touch screen TSP. Rx channels of the second touch sensing IC IC#2 are connected to the fifth to eight Rx lines Rx5 to Rx8 formed on the right half of the touch screen TSP.
As shown in FIGS. 2 and 3, differential amplifiers 11 to 14 may be connected to the Rx channels of the touch sensing ICs IC#1 and IC#2. An output terminal of each of the differential amplifiers 11 to 14 is connected to an inverting input terminal (−) via a capacitor C. Each of the differential amplifiers 11 to 14 amplifies a difference between an ith touch sensor signal input to the inverting input terminal (−) and an (i+1)th touch sensor signal input to a non-inverting input terminal (+) and outputs ith sensor signals S1 to S4, where ‘i’ is a positive integer. A noise having a similar magnitude may be applied to the adjacent touch sensors. Thus, as shown in FIG. 3, the differential amplifiers 11 to 14 amplify a difference between the signals received through the adjacent Rx lines and remove the noise. Further, the differential amplifiers 11 to 14 further increase signal components and may improve a signal-to-noise ratio (SNR).
However, a related art has the problem, in which the signal-to-noise ratio is reduced at a boundary between the touch sensing ICs IC#1 and IC#2. Signals including noises of the same magnitude have to be input to both input terminals of the differential amplifier, so as to increase the signal-to-noise ratio using the differential amplifier. As shown in FIG. 3, the differential amplifier 14 connected to the last Rx channel of each of the touch sensing ICs IC#1 and IC#2 is connected to one Rx line. The fourth Rx line Rx4 is connected to the inverting input terminal (−) of the differential amplifier 14, and a predetermined dummy signal D0 is applied to the non-inverting input terminal (+) of the differential amplifier 14. Thus, an output signal of the differential amplifier 14 includes an amplified signal component and an amplified noise component. Because of this, the signal-to-noise ratio of the touch sensors existing at a boundary between the left half and the right half of the touch screen TSP is less than the signal-to-noise ratio of the touch sensors at other positions of the touch screen TSP. As a result, as shown in FIG. 1, when the touch screen TSP is driven using the plurality of touch sensing ICs IC#1 and IC#2, it is difficult to decide the touch input in a middle portion of the touch screen TSP.
U.S. Publication No. 8,350,824 B2 disclosed a method for connecting two ICs to a large-sized touch screen and obtaining touch sensor data (hereinafter referred to as “boundary data”) at a boundary between the two ICs. A sensing method disclosed in U.S. Publication No. 8,350,824 B2 proposed a method for low-pass filtering the boundary data between the ICs and data adjacent to the boundary data and generating the boundary data using a low-pass filtering value as an average value, so as to obtain the boundary data. However, the sensing method has to compare the data adjacent to the boundary data and calculate the average value of the adjacent data, so as to obtain the boundary data. Hence, a processing amount of data increases, and data processing time increases. Further, when there is a large output deviation between the ICs, the accuracy of data is reduced.